1. Field of the Invention
The present invention relates to an evaporation apparatus, and more particularly to a linear evaporation apparatus capable of effectively enhancing the uniformity of an evaporated thin film and the utilization of an evaporation material.
2. Description of the Related Art
At present, different industries tend to use renewable energies to meet energy requirement, avoid energy shortage, and ensure the concept of business sustainability. For example, solar cell is one of the popular renewable energies. In addition to silicon-based solar cells and gallium arsenide (GaAs) solar cells, there is another type of potential solar cells such as copper-indium-gallium-selenium (CIGS) solar cells composed of Group I-III-VI2 elements having the features of high coefficient of optical absorption, excellent semiconductor property and flexible manufacture by substrates of different levels of hardness, so that the CIGS solar cell has become the type of solar cells with very high competitiveness in the solar cell industry.
The CIGS solar cell is produced by sequentially depositing a plurality of thin films with different functions on a substrate, and the substrate is generally made of a material containing sodium alkali glass (SLG), and composed of a Mo back contact, a CIGS absorber, a CdS buffer, an i-ZnO/AZO window and an Ni/Al front contact sequentially arranged from the top to the bottom of the substrate, wherein the Mo back contact and the i-ZnO/AZO window are formed by magnetron sputtering, and the CIGS absorber is formed by evaporation, and finally the Ni/Al front contact is deposited by electron beam evaporation, so as to complete the production of the CIGS solar cell.
In the evaporation CIGS absorber, evaporation materials are generally put into a plurality of containers, and a heater is provided for heating the containers, and—a CIGS thin film is formed on a substrate from the evaporation materials by a dot-pattern evaporation method. The dot-pattern evaporation method may be able to achieve the expected uniform evaporation effect in a small area, but the dot-pattern evaporation method is unable to form a CIGS thin film with uniform thickness for large continuous substrates. Since the evaporation point is generally situated at the center position of the substrate, the thickness of the CIGS thin film situated at the edge of the substrate is much smaller than the thickness at the center position of the substrate. In addition to the issue of the thickness uniformity of the CIGS thin film, the present evaporation equipments also has following drawbacks related to the control of the utilization of the evaporation materials, the durability of the evaporation source, and the stability and the evaporation speed of the evaporation process. 1. If an evaporation source device adopts an open design, the vapor distribution angle of the evaporation materials cannot be limited, so that an over-spilling condition may lower the utilization of the evaporation materials. Since the evaporation materials heated independently, molecules may collide and interfere with one another during the mixing and evaporation of the substrate, and the mixture of the evaporation materials may be non-uniform, and the cladding of CIGS thin films and the bonding of PN junctions.
2. As the quantity of evaporation materials gradually decreases with time during the manufacturing process, the liquid level of the evaporation materials drops to change the evaporation speed, so that the manufacturing process and composition cannot be controlled and quantified effectively. To manufacture large CIGS thin films and improve their uniformity, a linear evaporation method is generally adopted in the CIGS thin film manufacturing process, and the linear evaporation method is able to assure the uniformity of the large CIGS thin films by adjusting the area and shape of the evaporation port. As disclosed in P.R.C. Patent No. CN203128644 entitled “Linear evaporation source nozzle”, the linear evaporation nozzle comprises an injection hood, an injection board installed on the injection hood, an injection port formed along the longitudinal direction of the injection board, and a shielding plate installed at the injection port for dividing the injection port into two sections. During use, the injection hood is placed on a linear evaporation source. As disclosed in the aforementioned linear evaporation source nozzle, the thin film formed by the linear evaporation source nozzle is more uniform than that produced by the dot-pattern evaporation method in a large-area evaporation process, and the thickness of the thin film is still non-uniform. When several evaporation materials are mixed and used in the evaporation process, the non-uniformity of the mixed materials is still not improved significantly.
In the manufacture of an absorber for copper-indium-gallium-selenium thin film solar cells as disclosed in U.S. Pat. No. 7,194,197B1, and U.S. Patent Application Nos. 2008/0247738A1, 2008/0247737A1, 2008/0226270A1, 2010/0173440A1, 2010/0087016A1, 2009/0258476A1, 2009/0258444A1, 2009/0255469A1, 2009/0255467A1, U.S. Pat. No. 8,202,368B2, 2010/0159132A1 and 2010/0285218A1, when such manufacturing method is applied to the manufacture of thin films, several sets of independent linear evaporation sources and reactive evaporation sources are separated to mix the vapors produced by the linear evaporation source of different evaporation materials effectively with one of the reactive vapors such as selenium vapor, sulfur vapor, or antimony vapor or their mixture to produce a large thin film. However, the utilization of the evaporation materials in the evaporation process often has the following problems. 1. The evaporation angle of the linear evaporation source changes with the evaporation distance from the center of the linear evaporation source, and the linear evaporation sources will interfere with one another during the mixing and evaporation processes due to the changing evaporation angle of the linear evaporation source and the temperature of the manufacturing process, so that the uniformity of the thin film will be reduced significantly. To improve the uniformity of the evaporation, it is necessary to cover the non-uniform positions produced from the evaporation in order to have a better uniformity in the evaporation area. However, such method will lower the effective utilization of the evaporation materials. 2. The temperature of a general linear evaporation source such as copper, indium or gallium exceeds 1000° C. in the manufacturing process. To avoid the reactive vapor from being affected by the thermal field generated by the linear evaporation source such as copper, indium or gallium with a high temperature, or the positions of the independent linear evaporation source and reactive evaporation source from being obstructed, the reactive vapor must be filled in the whole chamber before the mixed vapors of the linear evaporation sources such as copper, indium or gallium can be reacted with the reactive vapor. Although a large quantity of the reactive vapor is filled up in the chamber, the quantity of the reactive vapor being actually reacted in the evaporation area is very limited, because a vast majority of the reactive vapor is condensed at a cooler chamber wall or extracted by the vacuum pump, so that the utilization of the reactive evaporation materials is reduced significantly.
To overcome the aforementioned and other drawbacks, the present invention provides a linear evaporation apparatus to improve the thickness of the thin film and the uniformity of materials in the evaporation process. In view of the aforementioned drawback of the conventional film deposition, the inventor of the present invention provides a method for stably evaporating uniform thin films to produce the thin films with high stability, uniformity and production quality.